(1) Field of the Invention
This invention relates to liquid systems and more particularly to a small storage vessel to allow for a relative small amount of liquid stored under pressure. This amount of stored liquid is to supply instant discharge from opening of a tap of a distribution system, and to allow for a measurable amount of liquid to be discharged from the system before requiring start up of the liquid supply pump. The system as a whole prevents the pump from cycling, that is quickly and repeatedly stopping and starting. Owners and Operators of water systems have ordinary skill in the art of this invention.
(2) Description of the Related Art
Many water pumps supply water to a system having irregular, intermediate use. Often these water pumps supply water into a reservoir such as a pressure tank. Water systems normally have a range of operating pressure. For example, the range of water pressure is set between 40 psi and 60 psi.
With small reservoirs the pressure drops quickly thus starting the pump motor. Then the reservoir is quickly filled and the pump motor stopped, resulting in the cycling condition.
Such a system as described is common on residential water systems having a separate water supply for every residence, as often occurs in rural areas. The problem could also exist in liquid systems other than water like gasoline fuel dispensing systems for example.
One solution to alleviate the cycling problem is to provide a large pressure reservoir. The reservoir stores a large amount of fluid to be used as the system pressure drops from 60 psi to 40 psi. In turn, as the pressure switch energizes the pump motor at 40 psi these large pressure tanks receive a large amount of fluid from the pump before the system is again filled to 60 psi and the pump is shut off. This allows for longer cycles with fewer starts and stops. These large pressure tanks are expensive, cumbersome, and maintenance intensive.
A second solution is to drive the pumps with a variable speed motor. As the pressure increases, the speed decreases by electrical control. By controlling the output flow from the pump to match the required usage, these devices eliminate cycling and almost eliminate the need for a pressure tank. In large systems enough taps are connected to require a constant flow from the supply. These new pump controls will keep the pump running continuously, supplying exactly the amount of flow being used. This eliminates the need for storing fluid in a pressure tank.
Another solution depends upon the fact that nearly all rotary pumps (non-positive displacement) have a reduced flow rate at high pressure. Therefore the system could be regulated to set a pressure cut off switch at a pressure slightly above the extreme reduced flow. However this might be far above the desired maximum pressure.
Yet another solution is to use an electric controlled valve to reduce the flow upon a signal produced by a high pressure in the system.
Perhaps a pump could be designed which had an adjustable flow rate at the same speed and a higher pressure. Such a pump might be developed by a pump having flexible blades.
Also pressure valves which at high pressure divert the flow to a by pass with a lesser flow rate.
The preferred solution is a pressure valve which reduces the flow at high pressure by forming a notch at the valve seat as described in my U.S. Pat. Nos. 5,988,984 and 6,109,296.
In smaller systems, zero flow is required at times when all of the taps are closed. Zero flow would require that the pump be off. If no fluid is stored under pressure as in a pressure tank, the slightest opening or drip from a tap would require restarting of the pump. Small bladder and diaphragm type pressure tanks are well known to the art. Such tanks are designed to express a small amount of fluid from an opened tap as pressure drops from 60 psi to 40 psi, and to receive a small amount of fluid as the pump fills the system from 40 psi to 60 psi. These small pressure tanks have a flexible membrane between the fluid in the tank and the air chamber. The air chamber is pre-charged to 38 psi creating a force that increases to 60 psi as the pump fills the fluid chamber until the pressure switch turns off the pump. The compressed air then forces fluid out of the fluid chamber as a tap is again opened. At 40 psi, just before the fluid chamber is emptied, the pump is again started.
Before this invention, the new pump controls greatly reduced the size of pressure tank required for a fluid delivery system. Still the small pressure tanks must be protected from freezing and vandalism. It is desirable that the tanks be hidden from beautified landscapes. Buried in the ground, hidden in the bushes, installed in crawl spaces, well houses, and vaults; even small tanks take up room.